GB1598101A - Liquid fuel consumption measurement systems - Google Patents

Description

(54) LIQUID FUEL CONSUMPTION MEASUREMENT SYSTEMS (71) We, R1CARDO CONSULTING ENGI NEERS LIMITED (Formerly called RICARDO & BR< Co., ENGINEERS (1927) LIMITED), a Com- pany registered under the laws of England, of Bridge Works, Shoreham-by-Sea, West Sussex BN4 5FG, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to systems for measuring the rate of consumption of liquid fuel by a prime mover, for example an internal combustion engine of spark- or compressionignition type, a gas turbine, or a Stirling cycle engine, all of which consume liquid fuels such as hydrocarbons and alcohols.

For test and development work on such prime movers it is necessary to know accurately the amount of fuel used in a given period of time or a given number of engine cycles. Both volumetric and gravimetric methods have been used since the earliest days of the I.C. engine, but the known methods have disadvantages which are becoming increasingly apparent in relation to modern needs and fuel systems. In particular volumetric systems are becoming less and less attractive, for various physical reasons.

The present invention is concerned with gravimetric methods of measurement. Some early gravimetric methods involved the suspension of a container of fuel from some form of balance, the engine drawing its supply of fuel from the container, and the time required for a given reduction in weight of the container under steady running conditions being measured. Various requirements and variations of this known basic method have been proposed, including arrangements in which the fuel is recirculated through the container during the test, but two effects must be guarded against here. One is the risk of vapour and bubbles from the return line being drawn into the feed line, and the other is the dynamic effect from the fuel flow within the container, which may cause spurious loading of the container.Some recirculatory systems involve very large recirculatory flow rates, up to 9 times the rate of fuel consumption, to eliminate air and fuel bubbles arising from temperature and pressure changes within the circuit of the angine's fuel injection system, so that such effects cannot be neglected. Furthermore it is difficult to check errors from this cause, so it is desirable to minimize them by appropriate design features.

According to the present invention, apparatus for the gravimetric measurement of the liquid fuel consumption of a prime mover, e.g. an I.C. engine, comprises a container for liquid fuel supported by a weighing device which is arranged to provice an output signal representing the weight of the supported container and its contents, an outlet pipe through which a flow of fuel is withdrawn from the interior of the container for circulation, and a return pipe, a small proportion of the circulating fuel flow being withdrawn in use for consumption by the prime mover and the balance of circulating fuel being returned to the container through the return pipe for recirculation, and in which the mouths of the outlet and and return pipes are located within the container in positions in which in use they will be submerged, and the outlet and return pipes and any pipe work associated therewith within the interior of the container are fixedly supported independently of the container, and which includes baffle means fixed with respect to the outlet and return pipes within the container and associated with the submerged mouths of the outlet and return pipes, the baffle means being arranged to guide their respective outgoing and incoming fuel flows to enter and leave the respective mouths in generally horizontal, generally radial directions, and to avoid the imposition on the container itself of any significant vertical components of hydrodynamic force due to such flows which would affect the said weight measurement, the baffle means being also adapted to screen from the mouth of the outlet pipe any gas bubbles entrained in the returned fuel flow entering the container from the return pipe, and to allow the majority of such bubbles to rise to the liquid surface in the container without being drawn into the outlet pipe.

In a preferred form of the invention. the weighing device comprises a load cell incorporating a force transducer arranged to produce an electrical output signal which is a function of the weight of the container and its liquid contents.

The output signal of the transducer constitutes a "ramp voltage", and circuitry can be provided for measuring the change in this voltage over a period of time, the fuel consumption measurement being calculated or derived from this measurement.

Moreover, the ramp voltage signal can be differentiated by suitable circuitry, or its change over a very short time interval, electrically gated, can be continuously evaluated, to give a continuous indication of the instantaneous flow rate. Such an indication is not obtainable from known gravimetric apparatus.

Means may also be provided for deriving from the output signal of the weighing device a direct measurement of the quantity of fuel consumed by the prime mover in a predetermined but variable interval of time.

Again, means may be provided for deriving from the output signal of the weighing device a direct measurement of the time taken for the prime mover to consume a predetermined, but variable quantity of fuel.

Where the prime mover is an internal combustion engine, operated in a predetermined sequence of load and/or speed conditions which are repeated as a series of operating cycles, means may be provided for deriving from the output signal of the weighing device the quantity of fuel consumed by the engine during a predetermined, but variable, number of the operating cycles.

In one construction of the invention, the outlet and return pipe arrangement within the container may comprise an open-ended outlet pipe extending below the minimum liquid level in the container and there surrounded by an open-ended return pipe of larger diameter whose open end is at a higher level than that of the outlet pipe, the outlet and return pipes entering the interior of the container without imposing vertical constraint on it, and the baffle means may comprise a radial baffle plate being spaced below the open end of the outlet pipe and a second and annular radial baffle plate being spaced below the open end of the return pipe above that of the outlet pipe which it closely surrounds, the two baffle plates being carried by one or other of the two pipes.This baffle system constrains the liquid flow into the outlet pipe and out of the return pipe to the generally radial direction avoiding axial flow components which might act on the bottom of the container and produce spurious load indications. Any air bubbles in the liquid returned from the return pipe will rise upwards and will not be entrained in the flow into the outlet pipe.

A controlled refill supply for the container is preferably provided.

Means is preferably also provided for controlling the maximum and/or minimum level of liquid in the container. Such means may comprise a pair of voltage comparators set to control a refill supply to the containers at predetermined maximum and minimum values of the output voltage of the transducer: alternatively a flat system with optical or other level sensors, or means for direct optical observation of the liquid surface, or hot thermistor immersion sensors set at different levels, may be provided for controlling the refill supply.

The supported container may itself be surrounded by an independently-supported outer vessel resting on a weight-sensing switch, and arranged so that in the event of an overflow from the supported container, the liquid will overflow into the outer vessel and cause the actuation of the switch, to interrupt the refill supply and prevent any further refilling until the fault is rectified and the system is reset.

The invention also comprises a method of operating the apparatus referred to, in conjunction with an internal combustion engine which draws its requirement of fuel for combustion from the circulating fuel flow, for example by running the engine, measuring the time required for the transducer output signal to vary by an amount corresponding to a predetermined change in the weight of the supported container, and its liquid contents i.e. a predetermined measurement a reading of the fuel consumption rate of the engine.

The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic elevation of an apparatus for measuring engine fuel consumption; Figure 2 is a diagram showing the refill system for the suspended container in Figure 1, this system having been omitted from Figure 1 for the sake of clarity; and Figure 3 is a diagram of the control circuit for the apparatus.

The instrument shown in Figure 1 is for measurement of the fuel consumption of an I.C. engine, and comprises a load cell 10 mounted on a cantilever arm 11 which itself is secured to a vertical post 12 upstanding from a heavy base 13. A weighing vessel 14 is freely suspended from the load cell 10 by a suspension 15, and its lower part is surrounded by an outer vessel 16 of larger horizontal dimensions, pivotally attached at 17 to the base 13 and resting on a weight switch 18. The heavy base 13 is itself resiliently supported on a fixed platform 19 by soft suspension units 20 giving the whole supported system a low natural frequency, to isolate the whole weighing system from possible external vibratory effects which could affect the accuracy of fuel weight measurement.

The load cell 10 incorporates a force transducer giving an electrical output in the form of a voltage which is a linear function of the load applied to the load cell. The transducer could be one of several known types, for example a bonded or unbonded strain gauge, a differential transformer, or a variable capacitance, combined with a suitable mechanical deflection system. So far, strain gauges, unbonded for very small loads and bonded to cantilever beams for greater values, have been found most suitable due to their superior temperature compensation characteristics. The output of the transducers is supplied to suitable electric circuitry (not shown) by which a read-out of the mass fuel consumption rate is provided, as referred to below.

The interior of the weighing vessel 14 which in use contains liquid fuel, contains a pipe assembly 22 forming part of a closed recirculation system from which the engine draws its fuel requirements. The recirculation system comprises an outlet 23 leading to the fuel intake of the engine, and a return pipe 24 through which the balance of recirculating fuel not withdrawn by the engine for consumption is returned into the weighing vessel 14. The oUtlet pipe 23 and return pipe 24 enter the weighing vessel 14 through oversize apertures in its upper part 14A, so that they do not touch the vessel 14, and have vertically down-turned open-ended end portions 23A and 24A which form the pipe assembly 22 and extend down nearly to the bottom of the weighing vessel 14.As will be seen, the vertical portion 24A of the return pipe is of larger diameter than that 23A of the outlet pipe and coaxially surrounds it, the open end of the return pipe portion 24A being spaced vertically above that of the outlet pipe portion 23A. An annular baffle plate 25 is fixed around the outlet pipe portion 23A above its open lower end and is spaced from and underlies the open end of the return pipe portion 24A. A circular baffle plate 26 is carried by a spider 27 fixed to the baffle plate 25, and is supported in a position spaced below and underlying the open end of the outlet pipe portion 23A.The system of baffles 25. 26 serves to ensure that fuel flow into and out of the outlet pipe portion 23A and return pipe portion 24A will be in symmetrical, generally radial directions, with substantially no axial components of dynamic loading such as might impinge on the weighing vessel 14 and cause spurious load indications. Moreover the annular baffle plate 25 separates the fuel flow paths entering and leaving the outlet and return pipes respectively, segregating the intake end of the outlet pipe portion 23A from the delivery end of the return pipe portion 24A, and thus ensures that any air or vapour bubbles in the recirculated fuel delivered into the weighing vessel through the return pipe 24 will rise upwardly in the vessel and will not be entrained in the fuel flow into the outlet pipe 23.The area of baffle 25, 26 also provides effective damping of movement of the freelysuspended measuring vessel, the pipe assembly 22 being fixed.

A fuel refill system is also provided for the weighing vessel 14, and comprises a refill pipe 30 leading from a fuel supply (not shown) into the interior of the vessel 14, again through an oversize opening above the highest liquid level, delivery of fuel through the pipe 30 being controlled by a normallyclosed solenoid valve 31. A suitable form of level control system is provided for controlling the operation of the solenoid valve 31 and determining the maximum and minimum liquid levels in the weighing vessel 14.

As mentioned, this may comprise a control circuit including a pair of voltage comparators set to control the refill supply in response to predetermined maximum and minimum values of the ramp voltage which is the output signal from the transducer.

The outer vessel 16 surrounds the lower part of the weighing vessel 14 without touching it, and provides security against accidental overflow of the weighing vessel.

The solenoid valve 31 is controlled by the weight switch 18 having an appropriate interval spring load, so that if the filling control system suffers a malfunction and the vessel 14 overflows the increased weight of the outer vessel 16 on receiving a small amount of the overflow will operate the weight switch 18 and close the valve 31, cutting off the. refill supply. A total power failure will also cause the valve 31 to cut off the refill supply.

The apparatus described may be operated in various ways, but a typical control system and method of operation will be described.

The electronic control and read-out system includes a digital switching system by which a desired fuel consumption mass can be preset, and an electronic clock with a digital display in units of 0. I sec. With the weighing vessel 14 initially filled to its upper limit of level the clock is set to zero and the load indicator display, which is responsive to the transducer output, shows a small negative reading, e.g. --10g. Suppose that the time taken for the engine to consume say 100g of fuel is required. The digital switching system is set to the desired fuel quantity, in this case 100g., and the engine is set to run steadily.

On a command to take a consumption reading the refill cycle is inhibited, and the level of liquid in the weighing vessel starts to fall as the engine consumes fuel from the recirculation system. As the level falls and the weight reading passes zero, the clock is automatically started. When the weight reading reaches the preset value of 100g. the clock is stopped, the refill system is re-activated and the level returns to the maximum and is maintained there by periodic opening and closing of the solenoid valve 31. All this is done automatically by the programmed control system. The time indication at which the clock was stopped remains displayed until a further reading command is given.

Figure 3 illustrates a suitable circuit for performing the above cycle. The strain gauge load cell 10 is indicated in the top left hand corner of Figure 3. It forms one arm of a Wheatstone Bridge 40 which is initially balanced. As the weighing vessel 14 fills, or empties, the resistance of the load cell 10 varies upsetting the balance of the Wheatstone Bridge. This means that a voltage difference proportional to the weight exists between the top and bottom corners (as drawn) of the - Bridge. This is fed into an operational amplifier 41 the output side of which is connected to a digital readout voltmeter 42. The circuit includes appropriate scaling factors.

The small circuit 43 immediately to the right of the Wheatstone Bridge is a conventional analogue differentiating circuit whose voltage output, including a suitable scaling factor, is read by a voltmeter 44 to indicate the instantaneous time rate of change of the Bridge unbalance volts. Thus the voltmeter dial 44 indicates the rate of fuel flow from the gravimetric weighing device via the pipe 23 to the engine or other device using the fuel.

The following standard symbols and notation are used in Figure 3 and in the description that follows: BCD = Binary coded decimal VSS = Ground or earth voltage VDD = Positive voltage source 1 within a shaped symbol having a dot at the output connection= a 'Nor' logic gate & within a shaped symbol having a dot at the output connection=an 'Nand' logic circuit.

& without a dot='And' logic circuit.

In considering the functioning of the circuit of Figure 3. two modes of operation must be distinguished: (1) the idling mode and (2) the measuring mode.

The BCD output of the DVM 42, together with a polarity signal from the DVM, is fed to a zero detector 47 and to two digital comparators 46 and 51, which compare the output with digital set-values set respectively by BCD switches 45 and 50. The switch 45 is used to set an arbitrary 'top level' for the fuel, slightly above the level at which the output of the DVM is zero. The switch 50 is used to set the quantity of fuel which is to be consumed by the engine during a timing period. By suitable gating, output signals from the zero detector 47 and the comparators 46 and 51 are produced on three lines, 100, 101 and 102. A signal on the line 100 indicates that the fuel level is at the arbitrary 'top level'; this corresponds to a small negative output from the amplifier 41.A signal on the line 101 indicates that the output of the DVM is zero, which corresponds to a fuel level slightly below the top level. This slightly lower level is the lowest point which the fuel level reaches in the idling mode, and is the starting or reference level for the measuring mode. A signal on the line 102 indicates that the fuel level has fallen below the reference level by an amount corresponding to the setting of the BCD switch 50; this corresponds to a positive output of the appropriate magnitude from the amplifier 41.

In the idling mode, the signals on the lines 100 and 101 are applied to the set' and 'reset' inputs of a latch 48, which controls the magnetic fuel supply valve 31. Thus, when the fuel level has fallen to the reference level, the latch is set and the valve opens, while when the fuel level has risen to the top level, the latch is reset and the valve closes again.

In this way, the fuel level is normally maintained between the reference level and the top level.

The circuit also includes a chain of three latches 103, 104 and 105, which control the sequence of events to occur when the fuel consumption of the engine is to be measured.

When a start button 52 is pressed, the first latch 103 of the chain is set. Also, through a NAND gate 106, a logic '1' signal is applied to a 'reset' input of a digital clock 53, and this signal is also supplied, through suitable gating, to set the latch 48, causing the valve 31 to open. The condition of both latches 48 and 103 being set serves to set the latch 104, and when this has occurred, the gates through which the 'set' input is applied to the latch 48 are disabled, so that the fuel level can now fall below the reference level, without the valve 31 opening to top up the container 14.

When the fuel level reaches the preset top level (it should be noted that the measuring sequence cannot be initiated if the fuel level is already at the top level, because the signal from the line 100 disables the start button 52), the latch 48 is reset and the valve 31 closed in the usual way; also, the combination of the latch 104 being set, and a signal appearing on the line 100, causes the third latch 105 to change state. This enables a NOR gate 107, through which the signal on the line 101 is connected to a 'start' input of the clock 53. Thus. as soon as the fuel level reaches the reference level, the clock 53 is started.

When the predetermined weight of fuel has been consumed, a signal appears on the line 102. This signal is applied to a 'stop' input of the clock 53, to the latches 103, 104 and 105 to return them to their normal states, and, through the necessary gating, to the 'set' input of the latch 48, to initiate refilling of the container 14. The time taken for the set weight of fuel to be consumed remains displayed by the clock 53, while the circuit returns to the idling mode.

A reset button 108 is also provided; this can be used to terminate a measurement cycle at any stage. Thus, the output of the reset button is gated together with the signal on the line 102, to have the same resetting effect; in addition, the reset button is connected to the NAND gate 106, to reset the clock 53 to zero.

Indicator lamps 55 and 56 are provided in association with the fuel valve 31, to indicate the filling and the overflow conditions.

Minor additions to the electronic circuitry will make it possible for a pulse emitted by the time clock 53 to stop the digital voltmeter weight reading after a preforseen time interval, i.e. a direct determination of the weight of fuel used in a fixed time interval after the weight passes through the initiating "zero" weight value following the pushing of the start button.

Similarly if ah engine on the test bed is programmed to execute a series of repeating load-speed-time cycles, for example when simulating standard driving cycles, a separate digital counter can be arranged to register the completion of each cycle of operation and after a predetermined number of cycles to emit a signal pulse to stop the weight indicating digital voltmeter 42. Thus the weight of fuel consumed during x operational cycles is determined.

The control system may also contain a circuit for differentiating the ramp voltage signal from the transducer 10, to produce a read-out indicating approximately the rate of flow of fuel being consumed by the engine.

This information could alternatively or additionally be presented to a data logger.

Thus the electronic control circuitry used to time and process the output signal from the strain gauge or other transducer may be used, either as described or with suitable modifications, to provide for a variety of options, including the following: 1. To measure the time required to consume a known weight of fuel.

2. To measure the weight of fuel consumed in a given period of time.

3. To enable the consumption of any selected weight of fuel, within the instrument's limits, to be timed, as compared with known equipment which is limited to timing the consumption of one or two specific weights only, the changing of which usually requires handling within the fuel measuring equipment.

4. When it is desired to measure the quantity of fuel used in a certain number of successive cycle changes in engine load and speed, as for example in certain exhaust emission tests, the instrument can be arranged to have a suitable cycle counting device to actuate the start and finish of the weight measurement. Thus an accurate determination of the fuel used in a given number of cycles of engine rotation can be determined.

5. By differentiating the weight/time output signal from the transducer, by either analogue or digital techniques, a derived signal can be displayed showing the (virtually) instantaneous fuel mass flow rate. This is very useful when adjusting engine controls.

WHAT WE CLAIM IS: 1. Apparatus for the gravimetric measurement of the liquid fuel consumption of a prime mover, e.g. an I.C. engine, which comprises a container for liquid fuel supported by a weighing device which is arranged to provide an output signal representing the weight of the supported container and its contents, an outlet pipe through which a flow of fuel is withdrawn from the interior of the container for circulation, and a return pipe, a small proportion of the circulating fuel flow being withdrawn in use for consumption by the prime mover and the balance of circulating fuel being returned to the container through the return pipe for recirculation, and in which the mouths of the outlet and return pipes are located within the container in positions in which in use they will be submerged, and the outlet and return pipes and any pipe work associated therewith within the interior of the container are fixedly supported independently of the container, and which include baffle means fixed with respect to the outlet and return pipes within the container and associated with the submerged mouths of the outlet and return pipes, the baffle means being arranged to guide their respective outgoing and incoming fuel flows to enter and leave the respective mouths in generally horizontal, generally radial directions, and to avoid the imposition on the container itself of any significant vertical components of hydrodynamic force due to such flows which would affect the said weight measurement, the baffle means being also adapted to screen from the mouth of the outlet pipe any gas bubbles entrained in the returned fuel flow entering the container from the return pipe, and to allow the majority of such bubbles to rise to the liquid surface in the container without being drawn

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. the line 101 is connected to a 'start' input of the clock 53. Thus. as soon as the fuel level reaches the reference level, the clock 53 is started. When the predetermined weight of fuel has been consumed, a signal appears on the line 102. This signal is applied to a 'stop' input of the clock 53, to the latches 103, 104 and 105 to return them to their normal states, and, through the necessary gating, to the 'set' input of the latch 48, to initiate refilling of the container 14. The time taken for the set weight of fuel to be consumed remains displayed by the clock 53, while the circuit returns to the idling mode. A reset button 108 is also provided; this can be used to terminate a measurement cycle at any stage. Thus, the output of the reset button is gated together with the signal on the line 102, to have the same resetting effect; in addition, the reset button is connected to the NAND gate 106, to reset the clock 53 to zero. Indicator lamps 55 and 56 are provided in association with the fuel valve 31, to indicate the filling and the overflow conditions. Minor additions to the electronic circuitry will make it possible for a pulse emitted by the time clock 53 to stop the digital voltmeter weight reading after a preforseen time interval, i.e. a direct determination of the weight of fuel used in a fixed time interval after the weight passes through the initiating "zero" weight value following the pushing of the start button. Similarly if ah engine on the test bed is programmed to execute a series of repeating load-speed-time cycles, for example when simulating standard driving cycles, a separate digital counter can be arranged to register the completion of each cycle of operation and after a predetermined number of cycles to emit a signal pulse to stop the weight indicating digital voltmeter 42. Thus the weight of fuel consumed during x operational cycles is determined. The control system may also contain a circuit for differentiating the ramp voltage signal from the transducer 10, to produce a read-out indicating approximately the rate of flow of fuel being consumed by the engine. This information could alternatively or additionally be presented to a data logger. Thus the electronic control circuitry used to time and process the output signal from the strain gauge or other transducer may be used, either as described or with suitable modifications, to provide for a variety of options, including the following: 1. To measure the time required to consume a known weight of fuel. 2. To measure the weight of fuel consumed in a given period of time. 3. To enable the consumption of any selected weight of fuel, within the instrument's limits, to be timed, as compared with known equipment which is limited to timing the consumption of one or two specific weights only, the changing of which usually requires handling within the fuel measuring equipment. 4. When it is desired to measure the quantity of fuel used in a certain number of successive cycle changes in engine load and speed, as for example in certain exhaust emission tests, the instrument can be arranged to have a suitable cycle counting device to actuate the start and finish of the weight measurement. Thus an accurate determination of the fuel used in a given number of cycles of engine rotation can be determined. 5. By differentiating the weight/time output signal from the transducer, by either analogue or digital techniques, a derived signal can be displayed showing the (virtually) instantaneous fuel mass flow rate. This is very useful when adjusting engine controls. WHAT WE CLAIM IS:

1. Apparatus for the gravimetric measurement of the liquid fuel consumption of a prime mover, e.g. an I.C. engine, which comprises a container for liquid fuel supported by a weighing device which is arranged to provide an output signal representing the weight of the supported container and its contents, an outlet pipe through which a flow of fuel is withdrawn from the interior of the container for circulation, and a return pipe, a small proportion of the circulating fuel flow being withdrawn in use for consumption by the prime mover and the balance of circulating fuel being returned to the container through the return pipe for recirculation, and in which the mouths of the outlet and return pipes are located within the container in positions in which in use they will be submerged, and the outlet and return pipes and any pipe work associated therewith within the interior of the container are fixedly supported independently of the container, and which include baffle means fixed with respect to the outlet and return pipes within the container and associated with the submerged mouths of the outlet and return pipes, the baffle means being arranged to guide their respective outgoing and incoming fuel flows to enter and leave the respective mouths in generally horizontal, generally radial directions, and to avoid the imposition on the container itself of any significant vertical components of hydrodynamic force due to such flows which would affect the said weight measurement, the baffle means being also adapted to screen from the mouth of the outlet pipe any gas bubbles entrained in the returned fuel flow entering the container from the return pipe, and to allow the majority of such bubbles to rise to the liquid surface in the container without being drawn

into the outlet pipe.

2. Apparatus as claimed in Claim 1, in which the weighing device comprises a load cell incorporating a force transducer arranged to produce an electrical output signal which is a function of the weight of the container and its liquid contents.

3. Apparatus as claimed in Claim 2, which includes means for measuring the change in the voltage of the transducer output signal over a period of time and means for calculating or deriving the fuel consumption measurement from this measurement.

4. Apparatus as claimed in Claim 3+ in which the means for measuring the change in transducer output voltage comprises a differentiating circuit, and in which the apparatus is arranged to give a continuous indication of the instantaneous flow rate of the feed to the prime mover.

5. Apparatus as claimed in Claim 3, in which the means for measuring the change in the transducer output voltage comprises means for continuously evaluating the change in the output voltage over very short, electrically gated periods of time, to give a continuous indication of the instantaneous flow rate of the feed to the prime mover,

6. Apparatus as claimed in any one of the preceding Claims which includes means for deriving from the output signal of the weighing device a direct measurement of the quantity of fuel consumed by the prime mover in a predetermined but variable interval of time.

7. Apparatus as claimed in any one of the preceding Claims, which includes means for deriving from the output signal of the weighing device a direct measurement of the time taken for the prime mover to consume a predetermined, but variable quantity of fuel.

8. Apparatus as claimed in any one of the preceding Claims, for use with an internal combustion engine which is operated in a predetermined sequence of load and/or speed conditions which are repeated as a series of operating cycles, which includes means for deriving from the output signal of the weighing device the quantity of fuel consumed by the engine during a predetermined, but variable, number of the operating cycles.

9. Apparatus as claimed in any one of the preceding claims, in which the outlet and return pipe arrangement within the container comprises an open-ended outlet pipe length extending below the minimum liquid level in the container and there surrounded by an open-ended return pipe length of larger diameter whose open end is at a higher level than that of the outlet pipe, the outlet and return pipes entering the interior of the container without imposing vertical constraint on it, and in which the baffle means comprises a radial baffle plate spaced below the open end of the outlet pipe and a second and annular radial baffle plate spaced below the open end of the return pipe above that of the outlet pipe which it closely surrounds, the two baffle plates being carried by one or other of the two pipes.

10. Apparatus as claimed in any one of the preceding Claims, which includes means for controllably refilling the container with fuel.

11. Apparatus as claimed in any one of the preceding Claims, which includes means for controlling the maximum and/or minimum level of liquid in the container.

12. Apparatus as claimed in Claim 11, in which the level control means comprises a pair of voltage comparators set a control a refill supply to the containers at predetermined maximum and minimum values of the output voltage of the transducer.

13. Apparatus as claimed in any one of the preceding Claims in which the supported container is itself surrounded by an independently-supported outer vessel resting on a weight-sensing switch, and arranged so that in the event of an overflow from the container, the liquid will overflow into the outer vessel and cause the actuation of the switch, to interrupt the refill supply and prevent any further refilling until the fault is rectified and the system is reset.

14. A method of operating the apparatus claimed in Claims 2 and 7, in conjunction with an internal combustion engine which draws its requirement of fuel for combustion from the circulating fuel flow, which method comprises running the engine, measuring the time required for the transducer output signal to vary by an amount corresponding to a predetermined change in the weight of the supported container and its liquid contents, i.e. a predetermined mass consumption of fuel, and deriving from this time measurement a reading of the fuel consumption rate of the engine.

15. A method of operating the apparatus as claimed in Claims 2 and 6 in conjunction with an internal combustion engine which draws its requirement of fuel for combustion from the circulating fuel flow, which method comprises setting the apparatus to a predetermined period of time, running the engine, and deriving from the change in the output signal of the transducer over the preset period of time a direct measurement of the quantity of fuel consumed during that period.

16. Apparatus for the gravimetric measurement of the liquid fuel consumption of an I.C. engine, substantially as specifically described herein with referance to Figures 1 and 2, or to Figutres 1, 2 and 3 of the accompanying drawings.